Electric coupling system



March 31, 1931. c, TRUBE 1,798,962

ELECTRIC COUPLING SYSTEM Original Filed July 14, 1928 Nbj--a I f} [I i v W A INVENTOR (ar/ 5 7;"ube, deceased, Sara/2 M 7r'ube,

ldm/b/klral'rzln ATTORNEYS Patented Mar. 31,

UNITED STATES PATENT OFFICE CARL E. TRUBE, DECEASED, LATE OF OSSINING, NEW YORK, IBY SARAH M. TRUBE,

ADMINISTBATRIX, OF OSSINING, NEW YORK, ASSIGNOR T HAZELTINE TION, A CORPORATION OF DELAWARE conrona ELECTRIC COUPLING SYSTEM Original application filed July 14, 1928, Serial No. 292,739, now Patent No. 1,763,380, dated June 10, 1930, and in Australia June 10, 1929. Divided and this application filed May 14, 1930. Serial No. 452,464.

This invention relates to electric coupling systems especially adapted for use with radio-frequency vacuum tube amplifiers, and more particularly to circuit arrangements 5. which operate most effectively over a relatively wide range in frequency. Theronpling systems are so arranged as to give a voltage ratio that varies automatically with the "frequency. The variation in voltage to ratio is accomplished in a primary circuit which includes a fixed self-inductance efi'ectively in parallel with one or more fixed apacities external to the main resonant circuit and which may be electrically isolated from is the main resonant circuit. The primary C11- cuitis resonant at a frequency lower (but preferably not greatly lower) than the lowest frequency within the range of the coupling system. Coupling systems answerso ing this description are descr1bed generally in the co-pending application for U. S. Letters Patent, Serial No. 292,739, filed July 14, i928, patented June 10, 1930, No. 1,763,f :8t), of which the present application 1s a d1v1- sion. The present application is confined to coupling systems in which the fixed selfinductance mentioned above is not electrornagnetically coupled to the main resonant circuit, or if incidentally present, the electromagnetic coupling is so small as to make no apparent contribution to the performance of the system.

The voltage ratio in an inter-tube coupling system effects the degree of amplification, the stability and the selectivity. At each frequency there is a particular ratio of output voltage to input voltage that 'Wlll g1ve the best compromise design. .Thls ratio varies rapidly with the frequency, being relatively high at high frequencies. This invention provides means for securing substantially the most desirable ratio at all frequencies without having any adjustable element except the tuning adjustment.

Referring to the drawings, Fig. 1 illustrates a vacuum tube and an electric coupling system embodying a simple form of this invention.

Fig. 2 illustrates a modification of Fig. 1 to having an additional fixed capacity.

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Fig. 3 illustrates a modification of Fig. 2 in which a two-coil transformerreplaces an auto-transformer.

Fig. 4 illustrates a modification of Fig. 3 by which direct voltage is removed from the fixed capacity.

The coupling system of Fig. 1 is tuned by a variable condenser C connected across the primary coil L and the secondary coil L in series. Ordinarily L should have much fewerzturns than L so that there is a high step-up voltage ratio between them. The path through the primary coil L from the plate of the vacuum tube to the filament includes also the fixed capacity G which is 65 external to the main resonant circuit C L L. In parallel with this path is a second path including the self-inductance L;,, the value of which is so chosen that its circuit (completed through C and L is resonant 7 at a frequency lower, but not greatly lower than the lowest frequency within the range of condenser C The circuit of L being completed through C and L is thereby coupled to the main resonant circuit C L L so that part of the current of C and L will flow through C and L this part of the current being limited mostly by the reactance of L Since the reactance of L varies directly with the frequency while that of C varies inversely with the frequency, the voltage across C, will rr idly fall ofi' relative to the voltage across L as the frequency rises. For a given output voltage E the voltage across L is very nearly independent of frequency, due to the electromagnetic coupling betwen L and L Hence the voltage E between the plate and the filament, being the sum of the voltages of C and L will fall off relative to E as the frequency rises, but less rapidly than the voltage across G alone. This is the condition which is desired and which results in the maintenance of a high degree of stability over the frequency range, together with hi h sensitivity and selectivity.

The operation of the circuit of Fig. 2 is essentially the same as that of Fig. 1, but here the circuit of L is completed through two parallel paths, that through O and that 100 fit) through C and L As before, this circuit L3, C C L should be made resonant at a frequency lower, but preferably not greatly lowcr,.than the lowest frequency within the range of C The voltage ratio E /E is obtained from a double step-up, first between C and the combination of C and C and then between L and L and, with the resonant condition just given, this voltage ratio will automatically vary with the frequency in the same manner as in Fig. 1. V

Fig. 3 differs from Fig. 2 only in that the primary coil L is not included in the main resonant circuit. Coil L should here have the same number of turns as in Fig. 2; while the secondary coil L should have the same number of turns as L and L combined, in Fig. 2. The remaining relations are the same as in Fig. '2.

In Fig. 3 the direct voltage of the plate battery B exists across condensers C and C.-., which is disadvantageous in that these condensers may break down. This difliculty is obviated in Fig. 4 by connecting the lower terminals of condenser G and coil L to the lower terminal of coil L instead of to the common lead at the bottom of the diagram. This connection does not affect the alternating-current relations of Fig. 4, which are identical with those of Fig. 3.

What is claimed is: i

l 1. A radio-frequency coupling system having input terminals and comprising a main resonant circuit including as elements a coil and a condenser, at least one of which is adjustable to tune the coupling system over a range in frequency, a circuit coupled to said resonant circuit, including a fixed capacity and a fixed self-inductance effectively in parallel and having a resonant frequency lower, but not greatly'lower, than the lowest frequency'within said range, said fixed capacity being external to said resonant circuit and said self-inductance not being electromagnetically coupled to said resonant circuit, a circuit element having a fixed voltage ratio relative to said resonant circuit, and a path through said coupling system between said terminals including in series said fixed capacity and said circuit element, whereby there is developed in said resonant circuit a resonant voltage whose ratio to the voltage between said terminals automatically rises when said adjustable element is adjusted for higher frequencies.

2. In a radio amplifier stage including avacuum tube having filament, grid and plate electrodes, an electric coupling system which comprises a main resonant circuit including as elements a coil and a condenser, at least one of which is adjustable to tune the couphng system over a range in frequency, a circuit coupled to said resonant circuit, including a fixed capacity and a fixed self-inductance effectively in parallel and having a.

resonant frequency lower, but not greatly lower,t han the lowestv frequency withm saidrange, said fixed capacity being external to said resonant circuit and said self-inductance qk.

not being electromagnetically coupled to said resonant circuit, a circuit element having a fixed voltage ratio relative to said resonantcircuit, and a path through said coupling system between said plate and said filament including in series said fixed capacity and said circuit element, whereby in the operation of the amplifier stage there is developed in. said resonant circuit a resonant voltage whose ratio to the voltage between the plate and the filament automatically rises when said'adjustable element is adjusted for higher frequencies.

3. In a radio amplifier stage including a vacuum tube having a filament, a grid and a plate, an electric'coupling system which comprises a main resonant circuit including as elements a secondary coil and a condenser, at least one of which is adjustable to tune the coupling system over a range in frequency, a circuit coupled to said resonant circuit, including afixed capacity and a fixed self-inductance effectively in parallel and having a resonant frequency lower than the lowest fre uency within said range, said fixed capacity being external to said resonant circuit and said self-inductance not being electromagnetically coupled to said resonant circuit, a primary coil electromagnetically coupled to said secondary coil, and a path through said coupling system between said plate and said filament including in series said fixed capacity and said primary coil, whereby in the operation of the amplifier stage there is developed in said resonant circuit a resonant voltage whose ratio to the voltage between the plate and the filament automatically rises when said adjustable element is adjusted for higher frequencies.

4. In a radio amplifier stage including a vacuum tube having afilament, a grid and a plate, an electric coupling system which comprises a main resonant circuit including as elements a coil and a condenser, at least one 7 of which is adjustable to tune the coupling system over a range in frequency, a fixed self-inductance connected between said plate and said filament, said self-inductance not being electromagnetically coupled to said resonant circuit, a fixed capacity extending from said plate to said resonant circuit, said self-inductance and all of the capacity associated therewith being resonant at a frequency lower, but not greatly lower, than the lowest frequency within said range, all of said capacity being external to said main resonant circuit, whereby in the operation of the amplifier stage there is developed in said main resonant circuit a resonant voltage whose ratio to the voltage between the plate and lit the filament automatically rises when said adjustable element is ad usted for higher frequencies. a

5. In a radio amplifier stage including a vacuum tube having a filament, a grid and a plate, an electric couplin system which com rises a main resonant circuit including as e ements a coil and a condenser, at least one of which is adjustable to tune the couling system over a range in frequency, a first fixed capacity and a fixed self-inductance effectively in parallel between said plate and said lament, said self-inductance not being electromagnetically coupled to said resonant circuit, a second fixpd capacity e xtending from said plate to sand resonant c1runit, said self-inductance and the capacity associated therewith being resonant at a frequency lower, but not greatly lower, than the lowest frequency within said range, all of said capacity being external to said main resonant circuit, whereby in the operation of the amplifier stage there is developed in said resonant circuit a resonant voltage whose ratio to the voltage between the plate and the filament automatically rises when said adjustable element is adjusted for higher frequencies,

d. it radio-freqency coupling system having input terminals and comprising a main resonant circuit including as elements a COll and a condenser, at least one of which is adjustable to tune the couplin system over a range in frequency, a secon clrcuit coupled to said niain resonant circuit, including a fined self-inductance elfectively in parallel with fixed capacity external to said main resonant circuit, said second circuit being resonant at a frequency lower, but not greatly lower, than the lowest frequencywithin said range, said self-inductance not being electromagnetically coupled to said main resonant circuit, a circuit element having a fixed volf tage ratio relative to said main resonant cirsuit, and a path throu h said coupling system between said terminals including in se ries said circuit element and at least a portion of said fixed capacity, whereby there is devcloped in said main resonant circuit a resonant voltage whose ratio to the voltage between said terminals automatically rises when said adjustable element is adjusted for higher frequencies.

i. lln a radio amplifier stage including a vacuum tube having a filament, a grid and a plate, an electric coupling system which comprises a main resonant circuit including as elements a coil and a condenser, at least one of which is adjustable to tune the coupling system over a range in frequency, a second circuit coufipled to said resonant circuit, including a xed self-inductance effectively in parallel with fixed capacity external to said main resonant circuit, said second circuit w being resonant at a frequency lower, but not greatly lower, than the lowest frequencycoupling system between said plate and said' filament including in series said circuit element and at least a portion of said fixed capacity, whereby in the operation of the amplifier stage there is developed in said main resonant circuit a resonant voltage whose ration to the voltage between the plate and the filament automatically rises when said adjustable element is adjusted for higher frequencies.

8. In a radio amplifier stage including a vacuum tube having a filament, a grid and a plate, an electric coupling system which comprises a main resonant circuit including as elements a secondary coil and a condenser, at least one of which is adjust: ble to tune the coupling system over a lung in frequency, a second circuit coupled to said resonant circuit, including a fixed self-inductance effectively in parallel with fixed capacity ex ternal to said main resonant circuit, said secand circuit being resonant at a frequency lower than the lowest frequency Within said range, said self-inductance not being electromagnetically coupled to said main resonant circuit, a primary coil electromagnetically coupled to said secondary coil, and a path through said coupling system between said plate and said filament including in series said primary coil and at least a portion of said fixed capacity, whereby in the operation of the amplifier stage there is developed in said resonant circuit a resonant voltage whose ration to the voltage between the plate and the filament automatically rises when said adjustable element is adjusted for higher requencies.

, 9. A radio-frequency coupling system having input terminals one of which is at a higher average radio-frequency potential than the other, said system comprising a main resonant circuit including as elements a coil and a condenser, at least one of which is adjustable to tune the coupling system over a range in frequency, a fixed self-inductance connected between said terminals, said selfinductance not being electromagnetically coupled to said main resonant circuit, a fixed capacity extending from the higher-potential one of said terminals to said resonant circuit, said self-inductance and all of the capacity associated therewith being resonant at a frequency lower, but not greatly lower, than the lowest frequency within said range, all of said capacity being external to said main resonant circuit, whereby in the operation of the amplifier stage there is developed in said main resonant circuit a resonant voltage whose ration to the voltage between said terminals automatically rises when said adjustable element is adjusted for higher frequencies.

10. In aradio amplifier stage including a vacuum tube having a filament, a grid and a plate, an electric coupling system which'comprises a main resonant circuit including as elements a coil and a condenser, at least one of which is adjustable to tune the coupling system over a range in frequency, a first fixed capacity and a fixed self-inductance effectively in parallel between said plate and said filament, said self-inductance not being electromagnetically coupled to said resonant circuit, a second fixed capacity extending from said plate to said resonant circuit, said selfinductance and the capacity associated therewith being resonant at a frequency lower,

but not greatly lower, than the lowest frequency within said range, all of said capacity being external to said, main resonant circuit, whereby in the operation of the amplifier stage there is developed in said resonant circuit a resonant voltage whose ratio to the I voltage between the plate and the filament automatically rises when said adjustable element is adjusted for higher frequencies, and whereby said fixed capacities effect a voltage step-up.

In testimony whereof I aflix my signature.

SARAH M. TRUBE,

Administmtrim of the Estate 0/ 011% E.

Trube, Deceased. 

